smart soot blower system
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1 Copyright © 2006 by ASME
Proceedings of ASME Power:ASME Power
May 2 -4, 2006, Atlanta, Georgia
PWR2006-88075
TARGETED BOILER CLEANING USING SMART SOOTBLOWER
Huiying Zhuang/Clyde Bergemann Sandip Parikh/Clyde Bergemann
Sandeep Shah/ Clyde Bergemann
ABSTRACT
A Smart Sootblower has been developed to meet the increasing
demand for advanced boiler cleaning equipment. Utility plants
are challenged to burn coals with severe slagging tendency.
Slagging condition may be significantly different from pendant
to pendant across the boiler. Conventional retractable
sootblowers cleans superheat and reheat pendants with even
intensity, resulting in over cleaning of some pendants and
“clinker” buildup in others. Modern instrumentation such as
SuperHeat Fouling Monitoring (SHFM) systems and Video
Cameras is able to locate the exact spot where the slag is
accumulated. With the help of these detention systems, the
Smart Sootblower, a multi-mode soot blower, is able to target
and adjust clean intensity based on slagging condition, thus
minimizing tube leakage and clinker formation. The Smart
Sootblower has two motors that independently control
translation and rotation motion. This allows the sootblower to
change helix for different cleaning in different sections of the
boiler. Operators can select zones require aggressive cleaning
and zones need less or no cleaning. Integration of SuperHeat
Fouling Monitoring (SHFM) system would provide operators
the knowledge of fouling condition and enable automatic
control of sootblowers for optimal performance. Actual
installations and data are presented.
INTRODUCTION
Burning coal in the power plants produces fouling and
slagging on the boiler surfaces. Deposits in boilers contribute to
boiler inefficiency, capacity reductions, and tube leakages.
Large clinker formations on the pendants can fall and break the
bottom tubes, causing millions of dollar losses. Boiler outages,
many related to ash and slag, are the major causes of lost
generation in the US fleet of coal-fired power plants. The cost
of these outages is in the billions of dollars per year in
additional expense for replacement power and the cost of
repairs. In particular, boilers switching from designed coals to
low sulfur western fuels such as Power River Basin (PRB) coals
often encounter severe slagging problems due to the lower ash
softening temperature of PRB coals.
The boiler cleanliness demands faced by today’s boiler
owners require a new solution for sootblowing. Operators are
facing dynamic and higher slagging rates due to fuel variability,
increased load and the like. Trying to control this slagging with
old technology often results in over consumption of the
sootblowing media and excessive erosion of boiler tube
surfaces. In many plants, the experience results in a minimal
improvement in heat transfer rate and a large increase in
operating and maintenance costs.
Slagging in the boiler has become a dynamic process.
Slagging condition may be significantly different from pendant
to pendant across the boiler. Large chuck of “clinker” may form
on pendants on one side of boiler while pendants on the other
side of boiler are relatively clean. Conventional retractable
sootblower technology, however, assumes that slag is evenly
distributed in the boiler. It cleans all the superheat and reheat
pendants with equal intensity, resulting in over cleaning of some
pendants and under cleaning of others. This eventually leads to
tube leakage or clinker formation.
Modern instrumentation such as SuperHeat Fouling
Monitoring (SHFM) systems are able to locate the exact spot
where the slag is accumulated. With the help of these detention
systems, plant operators know which area needs to be cleaned
more to eliminate the clinker, and which area require less
cleaning to avoid tube erosion. Consequently, a Smart
Sootblower, which is able to target and adjust cleaning intensity
based on slagging condition, is developed to help power plants
to optimize cleaning process, improve boiler reliability and
efficiency, reduce operating cost, and increase fuel flexibility.
2 Copyright © 2006 by ASME
OPERATIONAL THEORY
Targeted cleaning is achieved by integrating two innovative
technologies: Smart Sootblower and Super Heater Fouling
Monitor (SHFM). With the advent of Super Heater Fouling
Monitor (SHFM), real time feed back of boiler pluggage in
specific areas of the boiler is available. Based on information
received from the SHFM system a Smart Sootblower can be
utilized to go to specific area of the boiler and focus cleaning
onto the deposit. Consequently the cleaning efforts are
concentrated in areas where needed most.
Contrary to conventional retracts, the Smart Sootblower are
being steered to areas where plugging is most severe.
Conventional sootblowers only have one motor for both
transverse and rotational movement. They usually run at fixed
speeds and helix. As a result, the cleaning intensity is equal in
the entire cleaning path. The Smart Sootblower, however, has
two motors that independently control translation and rotation
motion (figure 1). This allows the sootblower to change helix
and speed for different cleaning zones in different sections of
the boiler.
With the Smart Sootblower, the jet impact time can be
increased by slowing the traverse speed down and cleaning with
a tighter helix. This allows operators to adjust the dwell time on
a deposit in a particular area to take full advantage of cleaning
capabilities that the blower offers. As a result, tenacious
deposits can be aggressively cleaned to improve boiler cleaning
and prevent large deposit build-ups. On the other hand in areas
with little deposits, cleaning intensity can be reduced by
operating with higher traversing speed and a less tight helix,
thus saving steam and avoiding tube erosion.
SHFM is the intelligence of the targeted cleaning system.
With the slag information provided by SHFM, operators
understand which zones require aggressive cleaning and which
zones need less or no cleaning. By integrating with SHFM
module, Smart Sootblower can also be automatically controlled
and optimized.
Clyde Bergemann and International Paper have pioneered
the use of strain gages to measure the ash accumulation on the
pendant surfaces. As described in our previous papers [1-3],
SHFM utilized strain gage technology to sense slag deposits on
the superheat and reheat pendants. Strain gages are installed on
the hanger rods of the superheat and reheat pendants [4] (figure
2). Data from each strain gage is converted to weight using the
stress strain relationship [5-6]:
S = Eε
Where,
S = Stress in pounds per square inch
E = Modulus of elasticity (30x106 for steel)
ε = strain in micro inches per inch.
Using the diameter of the rod a cross sectional area can be
calculated, and the stress is multiplied by the area of the rod.
The weight measurement can be started at any time within the
process and any subsequent readings indicate the change in
weight from starting conditions. Thus it is not necessary to start
from a totally unloaded rod.
SYSTEM DESIGN
The Targeted Boiler Cleaning system consists of two major
components: Smart Sootblowers and SHFM. SHFM detects the
location and quantity of slag deposit. Smart Sootlbower then
adjusts the cleaning intensity for different locations on the basis
of the slag information provided by SHFM. The heart of the
targeted sootblowing system is its zone-based cleaning (figure
3). The cleaning intensity depends on the position of the blower
and the severity of slag deposits. The operator defines zones
along the path of the lance and specifies the cleaning mode and
parameters in each zone (figure 4). For optimal performance,
the smart sootblower can automatically adapt mode and
parameter utilizing real time data from SHFM. The following
modes can be selected:
Variable Helix: This mode is similar to standard sootblower
operation, but the traversing speed and rotational speed may
both be set to define a helix the will provide approximate
cleaning for the conditions in that zone.
Intensive Cleaning: This mode can perform aggressive
cleaning. The lance can be virtually held in place while rotation
continues by selecting the number of rotations, the step
distance, and the interval between cleaning points.
Oscillation/ Partial Arc Cleaning: In this mode the
sootblower concentrate the blowing media on the area to be
cleaned by restricting its arc from a given starting angel through
a specified angle of rotation. Additionally, the control system
can vary the rotation speed to maintain a specified jet
progression velocity (JPV) (figure 5).
In addition, speed and direction control allow the operator
to speed up or slow down the blower to perform "repeat"
cleaning in an area without going to full retract position and
starting over again. For instance, the blower can be set up via
the local control panel to traverse in to the full insert position,
back out for say 5 feet and go back in again to the full insert
position. This method of control allows the plant to customize
or "focus" cleaning in known areas of ash buildup. Operators
can set up the sootblowers to clean in one direction and traverse
out at a higher speed to reduce blowing media consumption and
tube erosion.
The SHFM system includes dozens of strain gages and data
collection and processing system. The strain gages are installed
on the superheat support rods. A data amplifier receives data
from the strain gages and sends the data through an Ethernet
cable to a personal computer in the control room, which
contains the input processing and operator interface software.
Graphical representations of the pendants with color-coded
status as to weight loading from the gages constitute the
operator interface and provide the information of slag deposit
across the boiler (figure 6).
3 Copyright © 2006 by ASME
SYSTEM OPERATON
A Targeted Cleaning system was installed on a 700MW
B&W boiler that has experienced several clinker falls that
caused severe tube damages. Two Smart Sootblowers, one on
each side, were installed in the cavity between the Platen
Secondary Superheater Pendant and the Secondary Superheater
Pendant, just above the nose arc of the unit. This area did not
have any existing sootblowers and it was also an area of
significant slag formation. SHFM are also installed for slag
monitoring and Intelligent Sootblowing (ISB) control. Eight
strain gages were installed on hanger rods that support the
Platen Secondary Superheat Pendants, providing the location
and quantity of the ash accumulation across the boiler.
A performance test was conducted to evaluate the
effectiveness of the Targeted Cleaning system. The test consists
of two steps: baseline and Targeted Cleaning. In the baseline
step, the Smart sootblowers were run in the same way as
conventional sootblowers. They were operated with fixed speed
and helix in the entire travel. In the Targeted Cleaning step, the
clean intensity varies for different zones on the basis of
information provide by the SHFM system. Zones with more
weight were cleaned more intensely then zones with less weight.
The cleaning intensity of light-weight zones was slightly
reduced. Meanwhile, visual observation and flue gas
temperatures across the boiler are used to confirm the slag
information provided by strain gages.
Figure 7 shows the slag weight on the superheat pendants
measured by strain gages. The slag is not evenly distributed
across the boiler. Among the four gages on the left side, gage L-
1 and L-4 have less weight than gage L-2 and L-3. Similarly, for
the gages on the right side, gage R-1 and R-2 have more weight
than gage R-3 and R-4. Visual observation verified that the
pendants in the middle have less slag accumulation than
pendants on the sides. To further confirm the slag information,
temperature distribution across the boiler is also measured using
a hand-held laser pyrometer through eight observation ports in
the front wall. As shown in figure 8, the temperature profile is
very similar with the weight profile. This indicates that the
weight profile is correct because high flue gas temperature
usually increases slag accumulation.
Corresponding to the strain gage layout, the boiler is also
divided into eight cleaning zones. Each sootblower covers 4
zones. In the Target Cleaning test, the cleaning intensity for
heavy-weight zones was increased while the intensity for light-
weight zones was decreased. The cleaning intensity for different
zones is shown in table 1. Figure 9 compares the weight
reduction by using Targeted Cleaning method with the
conventional cleaning method. It shows that by using Target
Cleaning, much more slag is removed for zones that are were
cleaned more intensely. The zones include zone L-2 and L-3 on
the left and zone R-1 and zone R-2 on the right. In contrast,
there is no significant change of weight reduction for the rest
zones including R-3, R-4, L-1, and L-4 even though their
intensity was slightly decreased. This result also indicates that
those four heavy-weight zones are under cleaned in the
conventional operation since almost twice as much of slag can
be removed with an increased cleaning intensity. Those under
cleaned areas could potentially cause “Clinker” formation.
CONCLUSION
By combining the SHFM and Smart Sootblower
technologies, Targeted Cleaning system is able to focus on the
dirty areas and skip the clean areas, thus eliminating tube
leakage and clinker formation. The operational results in a 700
MW boiler have demonstrated that Targeted Cleaning cleans
more effectively than conventional cleaning method by
increasing cleaning intensity on dirty pendants. Installation of
Targeted Cleaning system results in reduced boiler downtime,
steam saving and increased boiler efficiency and fuel flexibility.
REFERENCES
[1] “Slag Monitoring at Georgia Power Plant Bowen”
IJPGC2003-40148, Charlie Breeding and Chris Bentley
[2] “Slag and Deposit Monitoring at TVA Cumberland”
PWR2004-52042, Charlie Breeding, Rabon Johnson, and Ben
Zimmerman
[3] “Ash Measurement at NRG Huntley Using High
Temperature Strain Gages”, PWR2005-50203, Charlie
Breeding, Joe Schmitt, and Huiying Zhuang
[4] United States Patent Number 6,323,442 issued November
27, 2001
[5] An Introduction to Measurements using Strain Gages,
Karl Hoffmann, 1998
[6] Strength of Materials, Ferdinand L. Songer, 1962, Harper &
Roe Publishers
4 Copyright © 2006 by ASME
Figure 1 Smartblower Dual Motor Carriage Assembly
Figure 2 Superheat Suspension Structure and Strain Gage Location
Lance Rotation
MotorTraverse and
Rotation Gearbox
Lance Rotation
Spindle Housing
Traverse Motor
Traverse
Pinion
Emergency Retract
Traverse Encoder
5 Copyright © 2006 by ASME
Figure 3 Mechanism of Zone-based Targeted Sootblowing
Figure 4 Cleaning Mode Selection for Different Zones
6 Copyright © 2006 by ASME
Figure 5 Oscillation/ Partial Arc Cleaning with Constant JPV
Figure 6 Slag Information across the Boiler Provided by SHFM
7 Copyright © 2006 by ASME
Figure 7 Display on the SHFM screen
1700
1800
1900
2000
2100
2200
2300
2400
1 2 3 4 5 6 7 8
Front Wall Observation Port No. (from left to right)
Te
mp
era
ture
(F
)
Figure 8 Temperature measurment across the boiler
8 Copyright © 2006 by ASME
Table 1 Cleaning Intensity for Different Zones
Zones L-1 L-2 L-3 L-4 R-4 R-3 R-2 R-1
Speed(fpm)
79.2 79.2 79.2 79.2 79.2 79.2 79.2 79.2Conventional
Cleaning
Helix(inch)
6 6 6 6 6 6 6 6
Speed(fpm)
95 62 62 95 95 95 62 62Targeted
Cleaning
Helix(inch)
6 3.8 3.8 6 6 6 3.8 3.8
0
100
200
300
400
500
600
Zone L-1 Zone L-2 Zone L-3 Zone L-4 Zone R-4 Zone R-3 Zone R-2 Zone R-1
We
igh
Re
du
ctio
n (
lb.)
Conventional Cleaning
Targeted Cleaning
Figure 9 Slag removed in conventional and targeted cleaning operation
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